1. Field of the Invention
The present invention relates to booster devices for initiation of low-sensitivity blasting agents. Such boosters are conventionally initiated by means of detonators or detonating cord.
2. Description of the Prior Art
In the past two decades, commercial mining, quarrying and construction blasting operations have undertaken the wide-spread substitution of low-cost "blasting agents" in place of the more traditional "dynamites." The blasting agents are of two basic types: ANFO, which is the trade term for a mixture of ammonium nitrate and fuel oil; and water-gel "slurries." ANFO is the more widely used, principally because of its low cost.
The change from dynamite to blasting agents has created a requirement for a new blasting product, known as a booster or primer (the terms are synonymous). While dynamite can be initiated satisfactorily by means of a blasting cap or detonating cord, the ANFO and slurry blasting agents are relatively insensitive materials which are not cap sensitive (that is, they cannot be detonated directly by blasting caps or by small amounts of ordinary detonating cord). The booster, therefore, is an intermediary explosive charge which in itself can be initiated by either blasting cap or detonating cord and, when detonated, produces sufficient shock and energy to cause the blasting agent to detonate.
When ANFO was first introduced, dynamite was commonly used as a booster in typical quantities of half a stick to three sticks in a bundle. Gradually, however, dynamite has been replaced by "cast" boosters, which consist of mixtures of TNT and PETN, which are high explosives that can be melted and poured into a mold. When cooled, the explosive solidifies into a somewhat homogenous mass. Such cast boosters are usually substantially solid cylinders two to four inches in diameter and a few inches high. Conventionally, a quarter inch diameter hole runs through the center of the cylinder either for placement of a blasting cp or to permit stringing on detonating cord. The weight of such cast boosters varies from one-third of a pound to over a pound.
Attempts have been made in the past to utilize detonating cord to directly initiate low sensitivity blasting agents, but such attempts were commercially unsuccessful because the proper configuration of the detonating cord was not known. Although these prior art detonating cord configurations could produce lower order detonation of low sensitivity blasting agents, they cannot produce a sufficient blast velocity with sufficient speed to be commerically useful in initiating low sensitivity blasting agents.